1. Field of the Invention
The present invention relates to methods, systems, and computer programs for dielectric etching of a semiconductor device, and more particularly, methods, systems, and computer programs for dielectric etching of a semiconductor device in a dual-module capacitively-coupled plasma (CCP) chamber.
2. Description of the Related Art
The manufacturing of integrated circuits includes immersing silicon substrates (wafers) containing regions of doped silicon into chemically-reactive plasmas, where the submicron device features (e.g., transistors, capacitors, etc.) are etched onto the surface. Once the first layer is manufactured, several insulating (dielectric) layers are built on top of the first layer, where holes, also referred to as vias, and trenches are etched into the material for placement of the conducting interconnectors.
SiO2 is a common dielectric used in semiconductor manufacturing. The plasmas used for SiO2 etching often include fluorocarbon gases such as carbon tetrafluoride CF4 and octafluorocyclobutane (C—C4F8), along with argon (Ar) and oxygen (O2) gases. The word plasma is used to refer to those gases in which the constituent atoms and molecules have been partially or wholly ionized. Capacitive radio frequency (RF) power coupling is often used for striking and sustaining the plasma because of the low dissociation rates obtained, favoring larger passivating molecules and high ion energies at the surface. To obtain independent control of the ion energy and the ion flux to the silicon substrate, dual frequency capacitive discharges (DF-CCP) are sometimes used.
Current plasma processing systems used in semiconductor wafer fabrication rely on highly interdependent control parameters to control radical separation, radical flux, ion energy, and ion flux delivered to the wafer. For example, current plasma processing systems attempt to achieve necessary radical separation, radical flux, ion energy, and ion flux by controlling a single plasma generated in the presence of the wafer. Unfortunately, chemistry dissociation and radical formation are coupled to ion production and plasma density and often do not work in concert to achieve the desired plasma processing conditions.
Some semiconductor processing equipment uses pulsed RF power sources. The current pulsed RF plasma technology does not provide control of the afterglow plasma during the RF OFF period when the plasma shuts off. Typically, during the RF OFF period, the plasma potential collapses and electrons escape to the walls of the chamber. In the afterglow, the electron density drops and the negative ion density increases. Then ions to escape to the walls as well. The charged species dynamics determines the distribution of charges inside the chamber and, therefore, its etching properties, but unfortunately these dynamics and fluxes of charged species are mostly uncontrolled. The only controls available for the afterglow period are the frequency of the modulation and the duty cycle.
Another problem with pulsed plasma technology is plasma re-ignition when the RF power turns on. If the plasma and the afterglow are extinguished completely during the RF OFF period, re-striking the plasma requires high RF voltage levels. Further, there can be trouble with RF issues, especially when operating at low gas pressures.
It is in this context that embodiments arise.